Today hip implant stems are typically a composite structure consisting of either a cobalt-chrome alloy or titanium alloy substrate that carries the patient's weight, with a textured surface coating composed largely of peaks and valleys to aid in immediate fixation and ultimately promote and facilitate long term osseointegration. See FIG. 1.
Today, the majority of implant coatings are textured, which are applied by hot plasma spray, vapor deposition (chemical and/or physical), or by sintering fiber mesh or beads. See FIG. 2.
These coatings processes leave a largely two-dimensional structure for the bone to grow around. There is no means for the bone to tunnel further into the coating so as to establish significant three-dimensional osseointegration. This may stifle or compromise long-term osseointegration. Additionally, the structures created using these technologies do not mimic the structure of trabecular bone which is three-dimensional, with interconnecting networks of pores with capillarity properties. See FIG. 3.
Recently, there have been advances in the creation of porous coatings that more accurately resemble trabecular bone. These porous surface coatings have interconnecting networks of pores which are similar to those of trabecular bone, and may serve to promote bone ingrowth deeper into the porous coating and provide better long-term implant fixation. There are several techniques known in the art for creating these porous coatings. One method is to coat a structure similar to trabecular bone, i.e., a polyurethane foam, with powdered titanium through low temperature arc vapor deposition (LTAVD) or chemical vapor deposition or sputtering, and then to sinter the resulting structure onto the substrate (hip implant). See FIG. 4.
Other methods include chemical vapor deposition of commercially pure tantalum onto porous carbon scaffold and then sintering the resulting structure onto the substrate (hip implant). See FIGS. 5 and 6.